added locale to account

New accounts will get locale set on create, old accounts will get locale set on certificate sign. It will only be set once in this release (no updates if it changes).

Requires https://github.com/mozilla/fxa-auth-db-server/pull/53

Closes #743
Do you want `typeof header === 'undefined'` here?

Hmm, ok. So if header was undefined, then it wouldn't pass the `!header` trick. Are we expecting that header could actually be the string 'undefined', and if so, where is that coming from? Am just trying to understand what we see here.